How many goals must Bayern Munich score against Barcelona to reach the Champions League final?

Pep Guardiola's side found themselves trailing Barcelona 3-0 going into their Champions League semi-final second leg.

Now the Bundesliga giants have a mountain to climb in order to make the final in the German capital next month. But then again, football is a funny old game.

Ahead of kick-off in Munich, the math is simple: Bayern need four goals without reply.

It's hardly worth dusting down your abacus to work that one out, but what if things were to get interesting in the Allianz Arena ?

Here are some of the potential scorelines that will see Bayern Munich reach June's Champions League final in Berlin:

Bayern Munich 4-0 Barcelona (Bayern win 4-3 on aggregate)

Bayern Munich 5-1 Barcelona (Bayern win 5-4 on aggregate)

Bayern Munich 6-2 Barcelona (Bayern win 6-5 on aggregate)

Bayern Munich 7-3 Barcelona (Bayern win 7-6 on aggregate)

And so on.

But that's not to say that Bayern simply have to score four goals in 90 minutes tonight.

Remember... a goal for Barcelona, at any time, rules out extra time.

Bayern Munich 3-0 Barcelona (extra time)

Bayern Munich 4-1 Barcelona (Barcelona win on away goals)

Bayern Munich 5-1 Barcelona (Bayern go through)

Bayern Munich 5-2 Barcelona (Barcelona win on away goals)

Bayern Munich 6-2 Barcelona (Bayern go through)

Bayern Munich 6-3 Barcelona (Barcelona win on away goals)

Bayern Munich 7-3 Barcelona (Bayern go through)

But don't forget the infamous 'away goals' ruling - which apply both after 90 minutes and extra-time - should Barcelona score this evening, and the aggregate scoreline finishes level, the Spanish giants would progress to the final. No matter how many goals Guardiola's side score.

To see the match go to penalties, here's what has to happen...

Bayern Munich 3-0 Barcelona (AET)

That's right. The complete reversal of last Wednesday's match is the only way this one can go to penalties.

All clear? Follow all the action from Munich with our Live Blog below to see what happens!